This invention relates to floating structures for use as waterborne leisure lands (artificial floating islands), floating piers and the like and also relates to unitary floats to be assembled into those structures.
Conventional floating structures are roughly divided into two; large structures of unitary construction and structures consisting of a number of small floats joined together. The latter structures are preferable because they are easier to manufacture and handle, e.g., in transportation and assembling. The floating units are joined by connector means in such manner that they are not disjoined by the action of wind or waves or by variation of loads they support and also that the vertical movements of the individual units are minimized. Usually eye plates are attached to the edges of the units for interconnection by means of bolts and nuts, chains, ropes, etc., or long iron bars are passed through a plurality of floats to interlock them together. A further alternative has been to unite the units with rubber belts. The joining means of eye plate-bolt-nut combination normally involve partial projections from the edges of the floats, providing considerable spaces among the adjacent units. This makes the assembly unable to maintain stability with irregular or ununiform loads. One recent approach to the problem is to form recesses in edges of floats and fix eye plates within the recesses. Interlocking with iron bars produces such an integrity that the assembly cannot be bodily hauled up from the water. Once the bars are pulled off, the units are difficult to reassemble. The disadvantage of the eyelet and rubber belt joints is that the parts are repeatedly subjected to varying loads due to vertical motion of the floats with waves and changes in loads and are eventually broken down.
In an effort to overcome these problems of the prior art, I proposed a floating structure and unit floats for assembly into the structure in Japanese Patent Application Public Disclosure (Kokai) No. 216386/1990. Products made in conformity with the embodiments described in the published specification have come into practical use. The invention remedied many of the shortcomings of the prior art floats and provided a floating structure easy to assemble and stable as assembled. The construction of the float disclosed in the specification will now be described with reference to FIGS. 1 and 3. As shown specifically in FIGS. 2 and 3, a plurality of floats 10, 10 of the same construction are formed from plastics, e.g., polyethylene. They are stepped so that they are mutually complementary in shape when arranged closely side by side and end to end. To be more exact, steplike lower extensions 14, 15 of each float 10 and overhanging upper extensions 16, 17 of each adjacent float 10 are superposed, as in FIGS. 1 and 2, with upright connecting posts 11 formed in one piece with the lower extensions inserted into corresponding connecting holes 19 formed in the upper extensions and fastened in place with bolts 13 threadedly engaged with nuts 18, or internally threaded portions of the connecting posts 11. The horizontal and vertical planes of the steplike configurations permit horizontal and vertical dispersion of the stresses resulting from the external forces due to vertical, horizontal, and other motions of the floats. Thus, the stress concentrations in the connections are substantially reduced and the stability of the assembled floating structure is enhanced. Given some allowances at the connections, the assembly can smoothly ride on the waves, even billows, with the overall stress concentration decreased to some extent.
However, the structure, in which the connecting posts 11 for joining use are molded in one piece with the float body from the same resin material, presents a problem. While the assembled structure is in use, the waving water surface causes the individual floats to drift toward and away from one another, with the result that stresses are repeatedly concentrated in the roots of the connecting posts. Experiments have revealed that this leads to cracking or breaking of the posts after long time service, necessitating the replacement of the entire float assembly even though the other parts are sound enough for continued use.
Another problem arises from the use of such a floating structure in a shallow water such as sandbank (e.g., about three meters deep). Sand then gains entrance into the gaps between the overlapping parts of the individual floats and abrades the roots of the connecting posts 11 rapidly with the aid of the changing load due to the incessant undulation of the water surface.